Method and arrangement for controlling a pumping station
A method and an arrangement for controlling a pump station includes measurement of the surface level of a liquid (465) by means of a sensor (452) and controlling the electric drive (401, 420, 430) of the pump (440) to a predetermined speed of rotation when a specific surface level value has been reached. This predetermined rotation speed value is preferably the rotation speed at which the ratio of the flow rate to the consumed power, i.e. the efficiency, is optimal. The measurement of the surface level and the related data processing for control of the pump are performed in a frequency converter (420) in conjunction with the control.
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The invention relates to a method and arrangement for controlling a pump station. The invention is most advantageously applied to a pump station connected to a tank or a reservoir.
Pump stations are used especially in municipal engineering, where they are typically connected to pure water tanks, rain water tanks or waste water reservoirs. The pump station is then intended to prevent the tank/reservoir from being emptied or filled depending on the application. Pump stations often comprise a measurement apparatus for determining the liquid surface level by measuring the liquid surface level and controlling the pump on the basis of the surface level.
Pump stations used for liquid transfer are usually composed of one or more electrically driven pumps. The electric drive consists of a suitable current supply circuit, an electric motor and a control unit suitable for controlling and/or adjusting the electric motor. The pump operates as a load on the electric drive. The most frequently used electric motor in pump systems is an alternating-current motor, especially an induction motor. An alternating-current motor is most conveniently controlled by a contactor, and then the motor is switched on/off in accordance with the liquid surface level. However, the control unit often consists of a frequency converter because of the benefits yielded by this. The speed of an electric motor is controlled with a frequency converter, which converts the frequency of the voltage supplied to the motor. The frequency converter, in turn, is adjusted by appropriate electric control signals.
A prior art pump station is illustrated in
The pump station illustrated in
Instead of surface level sensors of switch type, one could use e.g. a surface level sensor 152 based on pressure measurement, the sensor being located at the bottom of the tank and providing information about the surface level at all surface levels. In that case, one often uses a control arrangement in which a constant surface level is aimed at, with the rotation speed of the pump being continually adjusted in accordance with the liquid amount entering the tank or consumed from the tank.
In
Prior art solutions involve a number of drawbacks. Separate installation of measurement and control apparatus requires work at the mounting site, and the appropriate mounting site and arrangement for the equipment and the sensors often require specific planning for each installation. The conditions at the mounting site may also vary, and this requires the use of measurement and control devices of different types depending on the conditions at the mounting site.
In addition, in prior art solutions, the energy consumption and efficiency of the pump station depends on external factors, e.g. on the flow-time distribution of the liquid entering a tank to be emptied or of the liquid consumed from a tank to be filled. Thus, a pump station may have poor energy consumption efficiency. In addition, the operating speed of the pump may be—especially in continuously regulated systems—permanently so low that impurities, which risk to cause obstructions, gather in the piping because of the low flow. The drawbacks mentioned above increase the cost of installing the pump station, of the equipment and of the operation.
The purpose of the invention is to provide a new method and arrangement for controlling a pump station, the invention allowing the prior art drawbacks mentioned above to be eliminated or reduced.
The objectives of the invention are attained with a solution, in which the liquid surface level is measured, and when a given surface level value has been passed by, the electric drive of the pump is controlled to a predetermined rotation speed. This predetermined value of the rotation speed is preferably the rotation speed at which the rate of flow relative to the consumed power, i.e. the efficiency, is at maximum. The surface level is measured in connection with the control of the electric drive. The invention is applicable to pump stations comprising both one and more pumps.
The invention achieves significant advantages over prior art solutions:
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- the invention avoids acquisition and installation of measurement and control apparatus separately.
- since the pump is principally operated with optimal efficiency, energy savings are achieved.
- since the pump is principally operated at a rotation speed yielding a high flow rate, accumulation of impurities in the piping with consequent obstructions are avoided especially in waste water plants.
In the method of the invention for controlling a pump station, the pump included in the pump station transferring liquid from a tank or into a tank and said pump being controlled by an electric drive comprising a frequency converter
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- the surface level of the liquid in the tank is measured with a sensor,
- the pump operation is controlled on the basis of the measured surface level,
the method being characterised by - selecting a first value of the liquid surface level,
- selecting as the value of the first rotation speed of the pump substantially the value at which the ratio of transferred liquid amount to consumed energy is at maximum and
- monitoring the moment when the surface level reaches said first value of the liquid surface level from a predetermined direction, and controlling as a consequence of this detection the pump rotation speed to said first value of the rotation speed,
- said monitoring of the surface level and control of the rotation speed being performed in the frequency converter.
The frequency converter of the invention for electric drive of a pump station, the pump station comprising a liquid tank, a pump and an electric drive actuating the pump, is characterised by the frequency converter comprising
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- means for storing a first value of the liquid surface level,
- means for storing a first value of the rotation speed of the pump,
- means for measuring the liquid surface level on the basis of a signal received from a sensor,
- means for detecting the moment when the liquid surface level reaches said first value of the liquid surface level from a predetermined direction, and means for controlling the rotation speed of the pump to said first value of the rotation speed as a consequence of said detection so that said first value of the rotation speed is substantially the value at which the transferred liquid amount relative to the consumed energy is at maximum.
A number of embodiments of the invention are described in the dependent claims.
The invention and its other advantages are explained in greater detail below with reference to the accompanying drawings, in which
Step 204 comprises selection of the first and second value of the rotation speed and storage of the values. The first value of the rotation speed is preferably the value at which the pump station operates at optimal efficiency. The second value of the rotation speed is a value of the rotation speed higher than the first value, preferably the maximum rotation speed and/or the rotation speed achieving the maximum flow value.
Step 205 comprises measurement of the surface level of the liquid, such as water, present in the tank/reservoir. The measurement is performed by means of a signal received from the surface level sensor in the electric drive, preferably a frequency converter. Next follows monitoring of whether the predetermined first, second or third value of the surface level have been reached from the predetermined direction. The first direction is then the one into which the liquid level moves when the pump is switched off and the second direction is the one into which the pump seeks to move the liquid surface during operation. Thus, for instance, in pump installation for emptying the tank, the first direction is the direction into which the liquid surface rises and the second direction is the one into which the liquid surface sinks. Accordingly, in a pump installation for filling the tank, the first direction is the one into which the liquid surface sinks and the second direction is the one into which the liquid surface rises.
Step 206 comprises checking of whether the liquid surface has reached the first value of the surface level from a first direction. If this has occurred after the previous measurement, the rotation speed of the pump is set to a first value, i.e. the value at which its efficiency is optimal, 207. Unless the first value of the surface level has been reached from the first direction, the system proceeds to step 208.
Step 208 comprises checking of whether the liquid surface has reached the second value from a first direction after the previous measurement. If this is the case, the rotation speed of the pump is set to the second value, i.e. the value that is preferably the maximum rotation speed, or a rotation speed yielding the maximum flow value, 209. Unless the second value of the surface level has been reached from a first direction, the system proceeds to step 210.
Step 210 comprises checking of whether the first value of the liquid surface has been reached from a second direction after the previous measurement. If this is the case, the rotation speed of the pump is set to the first value, 211. Unless the first value of the surface level has been reached from a second direction, the system proceeds to step 212. Steps 210 and 211 are not necessary, but instead, as the pump moves the liquid surface, it may operate also at the second, i.e. higher rotation speed value until the third surface level value has been reached.
Step 212 comprises checking of whether the third value of the liquid surface has been reached from a second direction after the previous measurement. If this is the case, the pump is stopped, 213. Finally step 205 is resumed for a new measurement of the surface level.
One or more values of the liquid surface level are advantageously varied, because this avoids or reduces accumulation of any solid constituents contained in the liquid on the tank wall at the selected surface level.
It should be noted that the steps above could be performed in a different order or simultaneously. The comparison of the measured surface level with predetermined values can be performed e.g. by analogue comparators or by comparing digital values in a processor.
When the pump station comprises two or more pumps associated with the same tank, their controls are preferably arranged such that the pumps are activated in turn during pumping of liquid in small amounts, for the pumps to wear evenly and to avoid damage to any pump due to lack of use over a long period. When a large liquid flow is necessary, several pumps are advantageously used at the same time. However, it is possible to reach an adequate flow even in systems of several pumps by means of one single pump, and in that case the pumps would wear unevenly if they were not operated in turns.
When the liquid level has again risen to the first value of the surface level at moment c, pump M2 is activated in turn. The rotation speed of the pump is set to the first value of the rotation speed, at which the efficiency of the pump is at maximum (eff). As the liquid level reaches the third value of the liquid surface as a consequence of emptying at moment d, the pump M2 is stopped.
When the liquid level has again risen to the first value of the surface level at moment e, the pump M3 is activated in turn. The rotation speed of the pump is set to the first value of the rotation speed, at which the efficiency of the pump is at maximum (eff). As the liquid level reaches the third value of the liquid surface as a consequence of emptying at moment f, the pump M3 is stopped.
Subsequently, as the liquid surface next rises to the first value of the surface level at moment g, the pump M1 is activated again. As the liquid level reaches the third value of the liquid surface as a consequence of emptying at moment h, the pump M1 is stopped, etc.
As can be seen in
The controls of the different pumps are preferably coordinated by the control unit of the frequency converter of one pump. The data transfer between the different control units takes place by data transfer arrangements known per se, such as analogue/digital signals, by serial communications or via a field bus. In this case, the coordinating control unit of one pump transmits control data to the control units of the second/other pumps, which comprise means for receiving these control data from the coordinating control unit. Accordingly, data transfer arrangements between the control units can be used also for transferring surface level data from one control unit to another.
When the liquid surface level reaches the following limit value, also pump M3 is activated at moment C. Pump M3 is also preferably set to a second value of the rotation speed (max) at which the rotation speed and/or flow are at maximum. When all the three pumps have reached their maximum operation, the liquid level starts sinking. When the liquid level reaches the following level threshold value at moment D, the pump M1 is set to the first value (eff) of the rotation speed. When the liquid surface level has sunk to its lowest threshold value at moment E, all the three pumps are switched off.
The control unit 428 comprises preferably a processor 421, which monitors the liquid surface level and controls the functions of the frequency converter on the basis of the software. The control unit also comprises a memory unit 422 for storage of reference values of the surface level, selected values of the rotation speed of the motor and programs controlling the processor. The control unit also comprises a measurement unit 423, which receives and processes signals from one or more surface level sensors. The control unit is preferably connected also with an interface 424 having a keyboard and a display. The keyboard serves for feeding parameters used in the control and the display may show e.g. surface level data and information about the state of the electric drive.
The control unit may further comprise an input terminal for receiving alarm signals obtained from alarm sensors in the pump. Such alarm sensors typically consist of a temperature sensor or a leakage sensor. The control unit preferably controls the pump on the basis of a received alarm signal so that the control unit stops the pump after having received an active alarm signal. In such a situation, the control unit preferably transmits an alarm signal to the monitoring room. The control unit may carry out a similar alarm function to the monitoring room e.g. when the liquid surface value exceeds the predetermined alarm limit.
For controlling the processor, software has been stored in the memory of the control unit in order to enable the processor to control the functions of the frequency converter. The software has preferably been disposed to control the control unit to perform at least one of the following functions:
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- measurement of the liquid surface level on the basis of a signal from the sensor and control of the rotation speed of the pump on the basis of the liquid surface level,
- coordination of the control of at least two pumps so that the pumps are activated in turns,
- variation of at least one selected value of the liquid surface level in order to avoid that solid ingredients in the liquid gather on the wall of the tank at the selected surface level;
- performing an alarm function when the liquid surface level exceeds a predetermined alarm limit value, and
- monitoring the alarm signals from the alarm sensors of the pump and controlling the pump on the basis of the alarm signals.
It should be noted that the examples above use a surface level sensor, whose signal gives the value of the surface level each time the surface level is above the sensor. However, in the solution of the invention, surface level switches placed at the desired levels can, of course also be applied. The surface level can also be measured in many other ways, by means of an ultrasonic sensor, for instance.
It should also be noted, that, although an individual frequency converter having a separate control unit controls each of the pumps in the examples above, the frequency converters and/or control units of several pumps can naturally be combined into one single unit.
Although the major application of the present invention relates to water transfer, the invention can naturally be implemented in connection with other liquids as well.
The invention is not restricted merely to the embodiment example above, but many other modifications are conceivable without departing from the scope of the inventive idea defined by the independent claims.
Claims
1. A method for controlling a pump station, a pump included in the pump station transferring liquid from or into a tank and said pump being controlled by an electric drive comprising a frequency converter, the method comprising the step of:
- measuring the surface level of a liquid in the tank by means of a sensor (205),
- controlling the activation of the pump on the basis of the measured surface level (206-213),
- selecting a first value of the liquid surface level,
- selecting as the value of the first rotation speed of the pump substantially the value at which the amount of transferred liquid relative to the consumed energy is at maximum and
- monitoring the moment when the surface level reaches said first value of the liquid surface level from a predetermined direction (206) and controlling as a consequence of this detection the pump rotation speed to said first value (204, 207) of the rotation speed,
- said monitoring of the surface level and control of the rotation speed being performed in a frequency converter.
2. A method as defined in claim 1, characterised in that a tank is filled by means of a pump at a pump station, said predetermined direction being from the top towards the bottom.
3. A method as defined in claim 1, characterised in that a tank is emptied by means of a pump at a pump station, said predetermined direction being from the bottom towards the top.
4. A method as defined in claim 1, characterised in selecting a second value (202) of the rotation speed of the pump and in monitoring the moment at which the liquid surface level reaches the following second value (208) of the surface level from said predetermined direction, and as a consequence of this detection, the rotation speed of the pump is controlled to a second value (204, 209) of the rotation speed.
5. A method as defined in claim 4, characterised in that said second value of the rotation speed is the maximum rotation speed.
6. A method as defined in claim 1, characterised in that at least two pumps (M1, M2, M3) are controlled at the pump station so that the pumps are in operating turns (a-b, c-d, e-f, g-h) alternately.
7. A method as defined in claim 1, characterised in that at least two pumps (M1, M2, M3) are controlled at the pump station and a third value of the rotation speed is selected, and while the first pump is operating, the moment is monitored at which the liquid surface level reaches a third value (B) of the surface level from said predetermined direction, and as a consequence of this detection, the second pump (M2) is also activated.
8. A method as defined in claim 1, characterised in that said predetermined at least one value of the surface level and at least one value of the rotation speed are stored in the frequency converter of the pump station.
9. A method as defined in claim 1, characterised in that said measurement of the surface level is performed in the frequency converter on the basis of a signal received from the surface level sensor.
10. A method as defined in claim 1, characterised in that an alarm signal is received from the alarm sensor of the pump and the pump is controlled on the basis of the received alarm signal.
11. A method as defined in claim 1, characterised in that an alarm function is performed when the liquid surface level exceeds a selected alarm limit value.
12. A method as defined in claim 1, characterised in that at least one selected value of the liquid surface level is varied in order to avoid that solid constituents in the liquid gather on the wall of the tank at the selected surface level.
13. A frequency converter (420) for the electric drive of a pump station, the pump station comprising a liquid tank (460), a pump (440) and an electric drive (401, 420, 430) actuating the pump, characterised in that the frequency converter (420) comprises
- means (422) for storing a first value of the liquid surface level,
- means (422) for storing a first value of the rotation speed of the pump,
- means (423) for measuring the liquid surface level on the basis of a signal received from the sensor (452),
- means (421) for detecting the moment the liquid surface level reaches said first value of the liquid surface level from a predetermined direction and means (420) for controlling the rotation speed of the pump to said first value of the rotation speed as a consequence of said detection so that said first value of the rotation speed is substantially the value at which the amount of transferred liquid relative to the consumed energy is at maximum.
14. A frequency converter as defined in claim 13, characterised in that the pump of the pump station has been disposed to fill the tank, said predetermined direction being from the top to the bottom.
15. A frequency converter as defined in claim 13, characterised in that the pump of the pump station has been disposed to empty the tank, said predetermined direction being from the bottom to the top.
16. A frequency converter as defined in claim 13, characterised in comprising means (422) for storing the second value of the rotation speed and means (421) for monitoring the moment the liquid surface level reaches the following second value of the surface level from said predetermined direction, and means (420) for controlling the rotation speed of the pump to a second value of the rotation speed as a consequence of this detection.
17. A frequency converter as defined in claim 16, characterised in that said second value of the rotation speed is the maximum rotation speed.
18. A frequency converter as defined in claim 13, characterised in that the pump station comprises at least two pumps, the frequency converter being disposed to control the pump so as to set it in operating turn alternately with two or more other pumps.
19. A frequency converter as defined in claim 18, characterised in comprising means for transmitting control data to the frequency converter of a second pump and/or for receiving control data from the frequency converter of a second pump for controlling the operating turns of the pumps.
20. A frequency converter as defined in claim 18, characterised in comprising means for transmitting surface level data to the frequency converter of a second pump and/or for receiving surface level data from the frequency converter of a second pump.
21. A frequency converter as defined in claim 13, characterised in comprising a memory unit (422) for storage of said predetermined at least one value of the surface level and of at least one value of the rotation speed and also for storage of a program controlling the electric drive.
22. A frequency converter as defined in claim 13, characterised in comprising a measurement unit (423) for receiving a signal from the surface level sensor (452) and for determining the surface level on the basis of the received signal.
23. A frequency converter as defined in claim 13, characterised in comprising a terminal for connecting the surface level sensor.
24. A frequency converter as defined in claim 13, characterised in comprising a processor (421) for controlling the electric drive on the basis of the surface level data and on the basis of the program that controls the processor.
25. A frequency converter as defined in claim 13, characterised in comprising means for receiving an alarm signal from the alarm sensor of the pump and means for controlling the pump on the basis of the received alarm signal.
26. A frequency converter as defined in claim 13, characterised in comprising means for performing an alarm function if the liquid surface level exceeds a predetermined alarm limit value or if an alarm signal has been received from the alarm sensor of the pump.
27. A frequency converter as defined in claim 13, characterised in comprising software stored in the frequency converter for controlling the frequency converter to perform at least one of the following functions:
- measurement of the liquid surface level on the basis of a signal from the sensor and control of the rotation speed of the pump on the basis of the liquid surface level,
- variation of at least one selected value of the liquid surface level in order to avoid that solid ingredients in the liquid gather on the wall of the tank at the selected surface level;
- coordination of the control of at least two pumps so that the pumps are activated in turns,
- performing an alarm function when the liquid surface level exceeds a predetermined alarm limit value, and
- monitoring the alarm signals received from the alarm sensors of the pump and controlling the pump on the basis of the alarm signals.
Type: Application
Filed: Mar 15, 2005
Publication Date: Jul 19, 2007
Patent Grant number: 8545189
Applicant: ABB OY (Hesinki)
Inventors: Srikanth Venkatachari (Bangalore), Mikael Holmberg (Porvoo)
Application Number: 10/589,867
International Classification: F04B 49/00 (20060101);